The present invention relates to a circuit carrier, in particular a printed circuit board, having two metallic outer layers and at least one metallic intermediate layer. Insulating layers are arranged between the outer layers and the intermediate layer. At least one component to be cooled is arranged on at least one of the outer layers, and at least one cooling element is arranged on at least one of the outer layers. The cooling element is thermally coupled to the component to be cooled via at least one heat conducting path.
Circuit carriers of this type are generally known.
When heat arises in the electrical and electronic components arranged on such circuit carriers, such as printed circuit boards, it has to be dissipated. Since a component""s own surface does not suffice for this purpose, it is known in the prior art to arrange a heat sink on the component, or to thermally couple the component directly to a housing surrounding the circuit carrier. Furthermore, it is known to dissipate the heat that occurs via the circuit carrier. A number of possibilities are known in the prior art for this purpose.
For example, it is known to distribute the heat within the contact area on which the component is arranged (so-called thermal spreading). However, this measure has only a limited effect since the thermal resistance in the very thin contact area (approximately 25 to 200 xcexcm) is relatively large.
It is also known to dissipate the heat through the circuit carrier to a heat sink or the housing, which is arranged opposite the component on the other outer layer. The thermal coupling is in this case effected by means of metallic plated-through holes (thermal vias). This embodiment is restricted to configurations in which the component to be cooled is at the same electrical potential as the cooling element.
The object of the present invention is to develop a circuit carrier of the type mentioned in the introduction in such a way that the arrangement and linking of the cooling elements to a component to be cooled can be configured more flexibly. The object is achieved by causing the heat conducting path to run partly in the intermediate layer so that heat is transferred transversely in the intermediate layer. It is thereby possible for the heat to be dissipated not only in the outer layer on which the component is arranged but also laterally via the intermediate layer. This significantly reduces the thermal resistance during the transverse dissipation of heat.
If the intermediate layer is electrically connected to the component and/or the cooling element, the result is particularly effective if the intermediate layer is coupled to the component or the cooling element. In so far as is necessary for potential isolation, however, the intermediate layer can be electrically isolated from the cooling element or the component. If the electrical connection is at least one metallic plated-through hole (thermal via), the electrical connection can be created in a particularly simple manner during the production of the circuit carrier.
The component and the cooling element can be arranged on the same outer layer or on different outer layers. If the elements are arranged on the same outer layer, electrical isolation of component and cooling element can be realized in a particularly simple manner by arranging them on a respective contact areas, which are electrically isolated from one another by an isolation trench.
If the isolation trench is dimensioned in such a way that it has precisely the dimensions of the minimum permissible air and creepage clearance of the corresponding voltage class, comparatively good thermal coupling of the contact areas to one another is nevertheless produced. In this case, the coupling can be optimized by filling the isolation trench with an insulating medium, e.g. a soldering resist. This is because the insulating medium usually conducts heat considerably better than air, although nowhere near as well as metal.
If the elements are arranged on different outer layers, they can be arranged, offset relative to one another (which is necessarily the case when they are arranged on the same outer layer).
The component is thermally coupled to the outer layer particularly well if it is designed as a surface-mounted component. The coupling is even better if a contact body is arranged between the component and the outer layer.
The transverse transfer of heat can be increased by the circuit carrier having more than one metallic intermediate layer, within an insulating inner layer being arranged between two respective metallic intermediate layers and heat being transferred transversely in at least two of the intermediate layers. If the cooling element is a constituent part of a housing for the circuit carrier, the component can be cooled particularly effectively.